THIOL-MEDIATED INHIBITION OF FAS AND CD2 APOPTOTIC SIGNALING IN ACTIVATED HUMAN PERIPHERAL T-CELLS

Fas and CD2 receptors can transduce apoptotic signals through two inde pendent biochemical pathways, In this study, we first evaluated the ro le of intracellular GSH in these signaling pathways by inducing variat ions in the GSH pool of activated peripheral T lymphocytes, Increasing the concentration of intracellular GSH by means of N-acetyl-L-cystein e (NAG) and GSH ethyl ester (Oft) resulted in total protection against cell death, while inhibiting GSH synthesis with buthionine sulfoximin e (BSO) greatly enhanced cell sensitivity to Fas and CD2 apoptotic sig naling, The protection exerted by NAC and GSH Oft was essentially base d on their capacity to establish an intracellular reducing environment as it still occurred in BSO-treated cells, Thiol-containing compounds (cysteine, captopril, D-penicillamine and P-mercaptoethanol) inhibite d apoptosis while a series of non-thiol antioxidants (including catala se and vitamin E) failed to do so, suggesting that protection was seco ndary to thiols/disulfides exchange reactions at the level of cysteine residues in proteins and not to detoxification of reactive oxygen int ermediates, This conclusion was further supported by the finding that no enhanced generation of O-2(radical anion) and H2O2 could be detecte d in cells experiencing early stages of apoptosis such as a decreased concentration of intracellular GSH and cell shrinkage, Also, protectio n occurred in the presence of protein synthesis inhibitors, indicating that it was due to post-translational sulfhydryl redox regulation of critical molecules involved in the apoptotic cascade, These data sugge st that GSH, the most abundant intracellular thiol antioxidant, may be important in counteracting Fas- and CD2-mediated apoptosis of T lymph ocytes.